The previous discussions of geometric optics in this book disregard the wavelength and photon character of light. These discussions work with the artificial construct of light rays and show how light behaves on a large scale compared with the dimensions of interest.
Physical optics goes beyond ray tracings and vergence calculations and deals with the properties of light on smaller scales, providing explanations for many of the phenomena of the physical world, such as polarization, coherence, interference, and diffraction, for which the ray approximation of geometric optics is insufficient.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.